stunthanger.com
Engine basics => Engine set up tips => Topic started by: Dennis Toth on January 26, 2013, 06:42:20 PM
-
Guys,
I have been researching tank venting from muffler pressure and was wondering if others have tested using conventional vent pressure compared to uniflow muffler pressure? Looking at the Hayes tank thread indicated that a different approach could be viable. Seems that muffler pressure kinda defeats the uniflow venting by forcing gas into the tank rather then having the draw down pull air into the tank as needed. Putting the pressure into the uncovered vent seems to put a little more push that should be fairly constant. What have you experienced?
Best, DennisT
-
I use muffler pressure on uniflow and it suits me fine. I have never tried it non uniflow.
-
Uniflow works in the same manner on suction, muffler , or crankcase pressure. The pressure values are a bit different, but the physics are the same.
-
+1 Mike, but be prepared for a fight! It isn't "stunt physics"!!! LL~
-
What Mike said about uniflow.
I think there are two reasons that muffler pressure into a Hayes tank works, in spite of the lack of uniflow. First, because the muffler pressure is higher than atmospheric, the percentage of head loss that you get as the tank runs down is smaller than if you were running atmospheric pressure. Second, because the engines where those tanks seem to work best also seem to be less sensitive to head variation at the needle valve -- so they can absorb the pressure changes caused by no uniflow, and take them in stride.
Certainly the best Hayes tank setup I have is on an FP 20, which just goes the same speed no matter what you do for an absurdly wide range of needle valve settings. The fuel consumption goes up massively as you go richer and richer, but the speed stays constant until it's really blubbery.
I also suspect -- but am not enough of an engine guy to know -- that muffler pressure coupled with a rich needle setting tends to be self regulating. If the engine slows down a bit, the muffler pressure will reduce, that'll make the engine go a bit leaner, which will make the engine speed up. But I'm not going to make any bets on this one unless I do mucho testing.
-
...First, because the muffler pressure is higher than atmospheric, the percentage of head loss that you get as the tank runs down is smaller than if you were running atmospheric pressure....
Bingo!
See this: http://www.nclra.org/TechTopics/UniflowPhysics.pdf (http://www.nclra.org/TechTopics/UniflowPhysics.pdf) written in 1978, aimed at the racing crowd, but still exhibits the physics of the situation.
Bill